A Fundamental Study of Flow Mechanisms in Nanostructured Al Alloys and Intermetallic Compounds

摘要：轻量化铝（Al）的生产具有高强度，但在应力下具有足够的变形性而不断裂，是加速其在汽车和航空航天工业中的应用的技术挑战。早期的研究表明，通过高压和扭转（扭转）相结合的严重永久变形，显著的显微组织细化导致大块金属具有优异的硬度。因此，本项目的目的是科学地研究如何在传统铝合金和金属间化合物的微观组织细化过程中获得高强度和良好的失效延伸率。本课题的重要意义在于了解纳米Al体系在高压和扭转处理后的强化和流动机制，并确定如何克服大块纳米Al合金及其化合物的强度和成形性悖论。这些结果预计将产生重要的积极影响，因为对改善大块金属机械性能的机械理解将为铝合金应用和轻量化工程材料选择的发展策略提供新的机会。这项研究需要精通物理学、材料科学和机械工程等各个领域，这对研究生和本科生来说既具有挑战性，又有回报，他们将得到这项计划的支持。技术摘要：在铝合金和金属间化合物中实现高强度和高延展性是目前无法控制的。虽然高压扭转（HPT）的晶粒细化通常可以提高金属的硬度，但在金属材料中实现高强度和延展性的策略仅在有限的条件下可用：在沉淀硬化合金或含有高密度纳米孪晶的材料中。除了可时效硬化的组合物外，将它们引入具有高层错能的人工智能系统是一个重大挑战。因此，本项目的目标是了解超细组织在微观和宏观尺度上增强和塑性的塑性流动机制，并设计策略来提高HPT加工的超细晶Al体系的强度和延性。该项目将纳米晶体材料的冶金研究专业知识与先进的表征方法相结合，包括新型纳米压痕技术和最先进的x射线和电子衍射分析。这些技术允许识别复杂的金属流动并发织构变化的时间尺度下的环境和高温。这个项目的贡献是显著的，因为所获得的改善大块金属机械性能的科学知识可以扩展到广泛的多晶材料，这有望扩大我们目前的工程材料选择，并提高美国在先进制造业的竞争力。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical Abstract:The production of lightweight aluminum (Al) having high strength but sufficiently deformable without breaking under stress is technically challenging in manufacturing to accelerate their applications to automotive and aerospace industries. Early studies demonstrated that significant microstructural refinement through severe permanent deformation by a combination of high-pressure and twisting (torsion) leads to excellent hardness in bulk metals. Thus, the objective of this project is to scientifically investigate how to achieve high strength and good elongations to failure in conventional Al alloys and intermetallic compounds after the microstructural refinement process. The importance of this project is to understand the strengthening and flow mechanisms of the nanostructured Al systems after the high-pressure and torsion processing, and to determine how to overcome the paradox of strength and formability in bulk nanostructured Al alloys and its compounds. These results are expected to have an important positive impact because a mechanistic understanding of improving the mechanical properties in bulk metals will provide new opportunities for the development of strategies for the applications of Al alloys and lightweight engineering materials selections. The research requires proficiency in a variety of areas including physics, materials science, and mechanical engineering, making it challenging and rewarding for graduate and undergraduate students who will be supported by this program.Technical Abstract: Achieving both high strength and good ductility is currently not controllable in Al alloys and intermetallic compounds. Although grain refinement by high-pressure torsion (HPT) generally improves the hardness of metals, the strategies for achieving both high strength and ductility in metallic materials are available only under limited conditions: in precipitation-hardened alloys or in materials containing high densities of nano-twins. Except in age-hardenable compositions, it is a major challenge to introduce those into Al systems having high stacking fault energy. Thus, objectives of this project are to understand the plastic flow mechanisms for strengthening and plasticity in micro- and macro-scales in ultrafine microstructures, and to design strategies to increase both strength and ductility of ultrafine-grained Al systems processed by HPT. This project combines expertise in metallurgical research on nanocrystalline materials with advanced characterization methods of measurements by the novel nanoindentation technique and state-of-the-art X-ray and electron diffraction analysis. These techniques allow to identify the complex metal flow with concurrent texture changes in a time scale under ambient and elevated temperatures. The contribution of this project is significant because the acquired scientific knowledge of improving mechanical properties of bulk metals can be extended to a wide range of polycrystalline materials, which is expected to expand our current engineering materials selections and produce an increased U.S. competitiveness in advanced manufacturing.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.